1. Technical Field
The present invention relates to a functional element, a physical quantity sensor including the functional sensor, an electronic apparatus, and a mobile entity.
2. Related Art
Recently, for example, as a physical quantity sensor which includes a functional element for detecting physical quantities such as an acceleration and an angular velocity, there has become known a capacitance type acceleration sensor (hereinafter referred to as acceleration sensor) which includes a substrate, a stationary electrode fixed on the substrate, a movable electrode disposed so as to face the top surface of the stationary electrode, and an elastic support section for elastically supporting the movable electrode on the substrate so as to be displaced in a direction orthogonal to the top surface of the substrate (for example, JP-A-2012-181030).
In the acceleration sensor, the elastic support section includes a lower layer support section fixed on the substrate, an upper layer support section fixed on the lower layer support section, and a beam section which has an elongated shape along the top surface of the substrate, of which one end portion is coupled to the upper layer support section and of which the other end portion is coupled with the movable electrode.
FIG. 14A and FIG. 14B are schematic plan views showing a configuration of a main portion of an acceleration sensor according to the related art described above. FIG. 14A shows a still state and FIG. 14B shows an impacting state. Further, the X axis, the Y axis and the Z axis indicate coordinate axes which are orthogonal to each other.
As shown in FIG. 14, in the acceleration sensor 500 of the related art, the elastic support section 501 includes a lower layer support section 503 fixed on the substrate 502, an upper layer support section 504 fixed on the lower layer support section 503, and a beam section 506 which has an elongated shape along the top surface of the substrate 502 in the Y axis direction, of which one end portion is coupled with the upper layer support section 504 and of which the other end portion is coupled with the movable electrode 505.
With an acceleration applied in the Z axis direction (the direction orthogonal to paper surface), the acceleration sensor 500 is configured to detect a difference based on the variation of the capacitances between the movable electrode 505 and two stationary electrode sections 507 and 508 on the substrate 502 due to swinging of the movable electrodes 505 around the beam section 506 as an axis (by twisting of the beam section 506) in the manner of a seesaw in the Z axis direction, and thus to derive the acceleration from the detected result.
With reference to “FIG. 3”, “FIG. 7” and the like in JP-A-2012-181030, in the acceleration sensor 500, when a gap between the beam section 506 and the upper layer support section 504 is L1 and a gap between the upper layer support section 504 and the movable electrode 505 is L2 in the X axis direction, during the still state as shown in FIG. 14A, there is a relational expression, L1<L2.
In this state, as shown in FIG. 14B, in the acceleration sensor 500, when an impact is applied from outside in the X axis direction, that is, for example, when the impact is applied in the + (plus) X axis direction (the dashed line arrow), the movable electrode 505 is rapidly moved in the − (minus) X axis direction according to an inertia (the solid line arrow).
In this case, since there is the relational expression, L1<L2 in the acceleration sensor 500, the beam section 506 which was bent in the −X axis direction collides with a corner section of the upper layer support section 504, before the movable electrode 505 contacts the upper layer support section 504.
Herein, since the beam section 506 is necessarily twisted to cause the movable electrode 505 to swing in the manner of a seesaw in the Z axis direction, there is a certain constraint on rigidity of the beam section.
As a result, in the acceleration sensor 500, there is a problem that the collision described above may cause the beam section 506 to be damaged, and it is necessary to improve the impact resistance thereof.